The invention pertains to gun-aiming systems involving computation of the lead angle and ballistic drop by which, for ballistic reasons, the gun bore alignment must "lead" and be "above" a given sighted target when the gun is fired.
Gun sights are of non-computing and computing varieties. Generally speaking, non-computing sights are either "iron" sights or "optical" sights, with either of which the gunner manually moves the gun until the part of the sight or reticle that corresponds to his estimated range and lead angle is lined up with the target, before he fires the gun and selects another target.
Heavier guns, such as turret-mounted guns used in Abrams tanks and Apache helicopters, employ so-called computed aim-point sights, which incorporate sensors to obtain target range and velocity to compute an aim point. This type of sight is a gun director, which moves the gun to the correct firing position independent of the sight motion. The gunner can smoothly track the target, using the sight, essentially unaware of gun motion.
Between the above-noted extremes are guns, such as 0.50-caliber machine guns on helicopters, boats and land vehicles, as well as larger weapons such as recoilless rifles. In this category, the weapon is manually moved, being gimbal-mounted for two-axis freedom for orientation in azimuth and in elevation in response to torques supplied by the gunner. A computing sight for such a gun generally provides the gunner with two spots in the sight and is termed a "disturbed-reticle" sight. The first spot is on boresight and is used by the gunner to initially track the target, thereby providing information such as range and angular rate to a ballistic computer. After completing the computations, a second point (e.g., a reticle) is displayed to designate the bullet-impact point. The gunner then physically moves the gun and sight to place the bullet-impact point on the target and fires.
One form of disturbed-reticle sight uses a laser beam to project the spot on the target and is called an "aiming light". In this type of sight, and after computations have been completed, the operator must move the gun such that the laser-beam spot registers with the reticle that identifies the bullet-impact point. Stated in other words, once calculations have been completed to the point of displaying the target-impact point, the gunner must transfer his attention and the aiming of his laser spot, from the target to the target-impact point which has just appeared in his display.
For weapons in a relatively slowly evolving situation, such as a recoilless rifle firing at a tank, the additional time to reposition the weapon, after completing the calculations, is not critical. On the other hand, in the case of a gun mounted to a low-flying helicopter moving at 100 knots, a more rapid response is desired.